Fluid flowmeter

ABSTRACT

A fluid flowmeter includes a conduit through which fluid flows by way of an inlet and an outlet for flow rate measurement. A first transducer transmits signals to and receives signals from a second transducer by way of the conduit. A second transducer is spaced from the first transducer along the conduit and transmits signals to and receives signals from the first transducer. A detector detects the time of flight of the signals between the transducers in order to measure the flow rate of the fluid along the conduct. A rod extends along the conduit to provide an annular flow path along which the signals are transmitted.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fluid flowmeter particularly althoughnot exclusively of the ultrasonic axial flow type.

2. Discussion of the Background

Fluid flowmeters of the axial ultrasonic type comprise a conduit throughwhich, in use, a fluid flows by way of inlet means and outlet means forflow rate measurement, a first transducer for transmitting signals toand receiving signals from a second transducer by way of the conduit,the second transducer being spaced from the first transducer along theconduit for transmitting signals to and receiving signals from the firsttransducer and means for detecting the time of flight of the signalsbetween the transducers in order to measure the flow rate of fluid alongthe conduit.

A problem with fluid flowmeters of the above type is that there is atendency for spurious signal reflections to occur at the walls of theconduit. These interfere with the actual signal or at least providefalse or inaccurate time of flight readings and therefore false orinaccurate fluid flow rate measurements.

It is therefore an object of the present invention to alleviate theseeffects.

SUMMARY OF THE INVENTION

According to the present invention there is provided a fluid flowmetercomprising a conduit through which in use fluid flows by way of inletmeans and outlet means for flow rate measurement, a first transducer fortransmitting signals to and receiving signals from a second transducerby way of the conduit, the second transducer being spaced from the firsttransducer along the conduit for transmitting signals to and receivingsignals from the first transducer, means for detecting the time offlight of the signals between the transducers in order to measure theflow rate of the fluid along the conduit and means extending along theconduit to provide for the fluid an annular flow path along which in usethe signals are transmitted.

Preferably the means extending along the conduit comprises a rod whichsuitably tapers outwardly from its ends to form a section of maximumexternal diameter within the conduit.

Conveniently the rod comprises a number of interconnected sections ofdiffering external diameters.

In one embodiment the ends of the rod are conical but in this case therod is otherwise of constant external diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be particularly described withreference to the drawings in which:

FIG. 1 is a schematic side view of a first embodiment of the invention,

FIG. 2 is a schematic side view of a second embodiment of the invention,

FIG. 3 is a schematic side view of one end of a third embodiment of theinvention, and

FIG. 4 is a side view of one end of an alternative arrangement for FIG.1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 the fluid flowmeter illustrated is of the ultrasonicaxial flow type and includes a straight or linear conduit 1, havingfirst and second ends 2 and 3 in which are respectively mounted firstand second transducers 4 and 5. The transducers 4 and 5 are positionedto transmit ultrasonic signals along the conduit 1 towards the othertransducer and to receive such signals after transmission. The conduit Iis formed with fluid inlet means 6 which in this case takes the form oftwo diametrically opposed inlet tubes adjacent the first end 2 of theconduit 1. Similarly the conduit 1 is formed with fluid outlet means 7which also take the form of two diametrically opposed outlet tubes. Thetransducers 4 and 5 are each connected to a detector 8 for detecting thetime of flight of each signal through the fluid flowing in the conduit.The detector 8 incorporates an electronic processing apparatus wherebythe time of flight of a signal in one direction can be used with thetime of flight of a signal in the opposite direction to compute the flowrate of the fluid along the conduit. The detector 8 may also include anindicator (not shown) in the form of a visual display showing a volumeflow rate or total volume flow over a given period. Thus far the fluidflowmeter described is well known in the art and detailed description ofthe components and operation of the device is unnecessary.

However, the fluid flowmeter described also includes means in the formof a rod 9 which extends along the conduit 1 and provides for the fluidan annular flow path 10 along which, in use, the signals from thetransducers 4 and 5 are transmitted.

The rod 9, which is solid, tapers outwardly from its ends 11 and 12 viatapering sections 13 and 14 to a central section 15 of maximum constantexternal diameter. At this point of course the radius of the annularflow path 10 is at a minimum. The ends 11 and 12 of the rod 9 aremounted by means (not shown) to the internal wall of the conduit 1.

FIG. 2 is similar to FIG. 1 and similar components bear identicalreferences to the components in FIG. 1. The only difference in FIG. 2 isthe construction of the rod 20. This comprises a number of sections 21to 25 of differing external diameters. The longest section 21 is solid,also has the smallest external diameter and forms the axial centrepieceof the rod 20 and it also forms ends 11 and 12 of the rod 20. Theremaining sections 22 to 25 are tubular in form and they each sleeve theadjacent section of smaller external diameter, the section of smallerexternal diameter being longer than the adjacent section of largerexternal diameter. Here again the central rod section 25 is of maximumconstant diameter and the section 25 forms with the internal wall of theconduit a minimum annular flow path radius.

As with FIG. 1 the ends 11 and 12 of the rod are mounted by means (notshown) to the internal wall of the conduit 1.

FIG. 3 is also similar to FIGS. 1 and 2 and similar components bearidentical reference numerals to those in those figures. Here the rod 30is of constant diameter but each end 31 (only the left hand shown) is ofconical form. The conduit 1 has frusto-conical wall portion 32connecting it to the inlet means 6 (and to the outlet means 7 at theother end of the conduit 1). The conical ends 31 of the rod 30 and theinner wall 33 of the wall portion 32 is mirrored to reflect the beamsfrom the transducers in the manner shown by the arrows in the Figure,i.e. the beam is converted from a generally cylindrical initial form asit leaves the transducers into an annular form by reflection firstlyfrom the ends 31 of the rod 30 and then from the wall portions 32.

Referring to FIG. 4 which is similar to FIG. 1 and bears similarreference numerals, here the end 40 of the conduit 1 is offset from theaxis of the rod 9 and the transducer 4 is mounted at this end. A wallportion 41 of the conduit 1 is angled in such a manner so that signalsfrom the transducer 4 are reflected from the internal wall 42 of theportion 41 along the annular flow path 10 to be received by reflectionby the other transducer 5, the internal wall 41 being mirrored for thispurpose. The conduit 1 is similarly designed at the other end and theother transducer 5 is similarly mounted to transmit by reflectionsignals to transducer 4 which receives them by reflection from the wall41.

The transducer reflection arrangement described with reference to. FIG.4 can be incorporated into the arrangement shown in FIG. 2 as well inplace of the direct axial transmission and reception transducerarrangement shown.

The flowmeter shown in the figures can be used to meter gas flow in agas meter. In this case the flowmeter would be mounted inside a boxwhich would display externally the total quantity of gas consumed by theconsumer since installation of the meter. We have found that the annularflow passage formed inside the conduit by the rod appears to renderfluid flow more uniform within the conduit. This leads to a reduction inthe propagation of spurious signal reflections and therefore to moreaccurate fluid flow rate measurements.

The rod supports should ideally be mounted between the inlet and itstransducer and between the outlet and its transducer, i.e. out of thegeneral flow path of the fluid so as to avoid, in the case particularlywhere the fluid is gas, a build up on the supports of debris or lintcarried by the gas. Such build up, if allowed to occur, may eventuallyblock the flow path.

I claim:
 1. A fluid flowmeter comprising:a conduit through which fluidflows by way of inlet means and outlet means for flow rate measurement;a first transducer for transmitting signals to and receiving signalsfrom a second transducer by way of the conduit, the second transducerbeing spaced from the first transducer along the conduit fortransmitting signals and receiving signals from the first transducer;means for detecting a time of flight of the signals between the firstand second transducers in order to measure a flow rate of the fluidalong the conduit; and a rod extending along the conduit to provide forthe fluid an annular flow path along which the signals are transmitted,the rod comprising a number of sections of differing diameters andincluding at least one elongate section of constant diameter.
 2. A fluidflowmeter as claimed in claim 1, including a plurality of elongatesections each of a constant diameter.
 3. A fluid flowmeter as claimed inclaim 1, wherein the diameter of the rod tapers outwardly from its endsto form a section of maximum diameter within the conduit.
 4. A fluidflowmeter as claimed in claim 3, wherein the rod comprises a number ofinterconnected sections of differing diameters.
 5. A fluid flowmeter asclaimed in claim 1, wherein the rod comprises ends which are conical,the rod being otherwise of constant diameter.
 6. A fluid flowmeter asclaimed in claim 5 wherein otherwise the rod is of constant externaldiameter.
 7. A fluid flowmeter comprising:a conduit through which fluidflows by way of inlet means and outlet means for flow rate measurement;a first transducer for transmitting signals to and receiving signalsfrom a second transducer by way of the conduit, the second transducerbeing spaced from the first transducer along the conduit fortransmitting signals and receiving signals from the first transducer;means for detecting a time of flight of the signals between the firstand second transducers in order to measure a flow rate of the fluidalong the conduit; and means extending along the conduit to provide forthe fluid an annular flow path along which the signals are transmitted,wherein the rod comprises ends which are conical, with a remainingportion of the rod being of constant diameter.